The present invention relates to a safety switch mounted on a peripheral wall surface of a protective door of, for example, industrial machinery etc., and stopping a supply of power to the industrial machinery etc. when the protective door is opened.
Conventionally, the protective door etc. of industrial machinery has been provided with a safety switch preventing the machinery from being driven in situations where the protective door is not fully closed in order to avert accidents wherein a worker is injured as a result of entrapment in the machinery. As an example of this type of safety switch, the safety switch disclosed in Patent Document 1 is provided with a lock mechanism that mechanically locks an actuator in the safety switch after the actuator having been inserted thereinto, thus preventing extraction of the operating key.
The safety switch provided with this lock mechanism is configured such that, for example, by providing an actuator in a protective door in the form of protrusion, and the switch main unit in the position where the actuator is inserted into the switch main unit through an insertion opening with the protective door closed, the actuator is inserted into the switch main unit through the insertion opening when the protective door is closed. Then, a cam-like plate (driving cam) is rotated as a result of insertion of the actuator, and as a result of the cam-like plate rotating, a cam follower pin that is in sliding contact along the respective cam openings are guided to a guide portion of a pin guide plate. A switching member, which integrally includes the cam follower pin, is caused to move as well so that a switching section is switched.
Also when the cam-like plate rotates as a result of insertion of the actuator, a locking bar of a lock lever (lock member) that is rotationally urged by an elastic member constantly abuts while making sliding contact with the cam-like plate in a substantially circular shape. When the cam-like plate is rotated to the position capable of switching the switch section, the lock lever rotates so that the locking bar opposes and engages with an engaging step section. Accordingly, the rotation of the cam-like plate as a result of motion of the actuator toward a withdrawal direction is blocked by the engaging step section abutting the locking bar, which mechanically locks the actuator to prohibit motion thereof toward a withdrawal direction, namely opening of a protective door. Then, for example, when the industrial machinery stops and a solenoid provided in a solenoid unit of the lock mechanism is operated due to input of a signal detecting the stoppage, the lock lever is operated against a urging force of the elastic member by the working rod of the solenoid, and the locking bar moves away from the engaging step section, thereby releasing the lock.
Next, the solenoid unit is described in detail with reference to FIG. 13. As shown in FIG. 13, a normally-open switching contact 124 and a normally-closed switching contact 125, which open and close in a manner coupled with the motion of the working rod 127a that moves as a result of the solenoid 127 being operated, and respectively become in an open and a closed in a locked state, which is a condition when a supply of power to the solenoid 127 is shut off. Also, an operation member 127b is connected to the working rod 127a, and the operation member 127b is engaged with a lock lever 127c. The operation member 127b moves pursuant to the motion of the working rod 127a that moves as a result of the solenoid 127 being operated, and the lock lever 127c moves in a coupled manner with the motion of the operation member 127b, and the engagement condition between the locking bar of the lock lever 127c and the engaging step section is released. It should be noted that FIG. 13 is a cross-sectional view showing a solenoid unit of a conventional safety switch.
Operations of the normally-open and normally-closed switching contacts 124 and 125, the operation member 127b, and the lock lever 127c are described in detail. Each of the normally-open and normally-closed switching contacts 124 and 125 includes a movable contact and a fixed contact. They are also provided with a first and a second link member, respectively, for moving the movable contacts by transmitting the motion of the working rod 127a of the solenoid 127 to the movable contacts. When the solenoid 127 is energized, the working rod 127a moves in the direction of the arrow ON and along with this the first and second link members also move in the direction of the arrow ON, and accordingly the movable contacts also move in the direction of the arrow ON. As a result, the movable contact and the fixed contact of the normally-open switching contact 124 contact each other, thereby putting the normally-open switching contact 124 in a closed condition, while the movable contact and the fixed contact of the normally-closed switching contact 125 are separated, thereby putting the normally-closed switching contact 125 in an open condition. Then, along with the working rod 127a moving in the direction of the arrow ON, the operation member 127b also moves in the direction of arrow ON. Pursuant to the motion of the operation member 127b in the direction of the arrow ON, the lock lever 127c engaged with the operation member 127b moves so that the safety switch becomes an unlocked state. Also, when a supply of power to the solenoid 127 is cutoff, along with the working rod 127a moving in the direction opposite to the arrow ON due to the urging force of a return spring (not shown), the first and second link members and the movable contacts move in the same direction as the moving direction of the working rod 127a, thereby putting the normally-open and normally-closed switching contacts 124 and 125 in an open and a closed condition, respectively. In addition, the operation member 127b moves in the same direction as the working rod 127a, and the lock lever 127c moves in a coupled manner with the motion of the operation member 127b. As a result, the locking bar of the lock lever 127c and the engaging step section become engaged so that the safety switch becomes a locked state. By monitoring the open-close conditions of the normally-open and normally-closed switching contacts 124 and 125, the lock condition of the lock mechanism can be detected.    Patent Document 1: JP H6-76675A ([0008] to [0009], FIG. 1)